Seat suspension vibration damper

ABSTRACT

A vibration damper module is described with a first member adapted for coupling to one of the vehicle and seat, and a shock absorber adapted to be coupled to the other of the vehicle and seat. The first member may take the form of a housing within which the shock absorber is substantially disposed. A latch selectively couples and decouples the housing to the shock absorber to respectively apply and relieve the application of the dampening force from the shock absorber to the seat which dampens vibrations in the seat. The shock absorber may include an external housing carrying a latch gripping surface, such as a plurality of teeth. The latch may comprise at least one latch arm having a latch surface. The latch arm may be shifted to a first position in which the latch surface and latch gripping surface are engaged to couple the first member to the shock absorber and to a second position wherein these components are disengaged. The latch arm may be pivoted to the housing with the housing also pivoted to one of the vehicle and seat. The shock absorber may also be slidably coupled to the housing. In addition, the shock absorber may apply a non-linear dampening force to the seat when the latch arm is in the first position.

BACKGROUND OF THE INVENTION

The present invention relates to a seat suspension vibration damper fordampening vibrations of a vehicle seat.

Numerous vehicle seat suspensions are known, including those having airbag or air spring suspensions for resiliently supporting a seat in aselected position. In such suspension systems, pressurized air isdelivered to or exhausted from the air bag to adjust the elevation ofthe seat. The use of an air bag permits upward and downward vibrationsof the seat. To counteract these vibrations, shock-absorbing cylindershave been used to dampen the seat vibrations.

In one known approach, as the elevation of the seat suspension ischanged by inflating or deflating the air bag, the shock absorbingcylinder has a piston supporting rod which extends or retracts,depending upon the direction in which the seat elevation is changed. Inthis approach, the shock absorbing cylinder must be capable of extensionand retraction throughout the entire range of seat elevation adjustment.In addition, these seat suspension systems are understood to use shockabsorbing cylinders with pistons that apply a constant dampening forceover the full stroke of the piston. If the dampening force werenon-constant in such systems, problems would ensue. For example, in suchsystems a non-constant dampening force would mean that the ride providedby the seat would vary depending upon the seat elevation.

U.S. Pat. No. 3,951,373 illustrates one form of seat suspensionutilizing a shock absorbing cylinder and an air bag or air spring. Inthis construction, the shock absorber is understood to have a strokewhich is capable of extending and retracting throughout the full rangeof seat height adjustment. However, in this construction, a hand knobmay be operated to adjust the throw of a shaft to thereby change theeffective length of the shock absorber.

Although numerous seat suspension systems are known and a number of themhave mechanisms for dampening seat vibrations, a need neverthelessexists for an improved vibration damper for a seat suspension systemhaving new and non-obvious differences from vibration dampers used inknown systems.

SUMMARY

A vibration damper is described for use in seat suspension systems suchas those of the type which support a seat above the floor of a vehicle,the seat being raisable and lowerable to support the seat at variousselected elevations relative to the floor of the vehicle, and whereinmovement of the seat from a selected elevation in response to vibrationsis permitted. The vibration damper is operable to dampen these seatvibrations when the vibration damper is operatively coupled to the seatsuspension system. In one illustrated form, the vibration dampercomprises a self-contained module which is convenient to install in aseat suspension system. Also, removal thereof, for example in the caseof repair or replacement, is relatively convenient.

In one illustrated embodiment, the vibration damper includes a firstmember adapted for coupling to one of the vehicle and seat. The firstmember may comprise a housing or may take other configurations. Thephrases “for coupling to” or “coupled to” one of the vehicle and seatincludes direct and indirect connection to one of these components. Forexample, the first member may be connected to a base or other componentof a seat support which is affixed to the vehicle. Alternatively, thefirst member may be directly or indirectly connected to the seat, forexample to a platform or seat support upon which a seat is mounted ordirectly to the seat. In addition, the vibration damper of thisembodiment includes a shock absorber adapted to be coupled to the otherof the vehicle and seat, again, direct or indirect coupling iscontemplated. Moreover, a latch is adapted to selectively couple thefirst member to the shock absorber such that when the shock absorber andfirst member are coupled together the shock absorber applies a dampeningforce to the seat. In addition, when the shock absorber and first memberare decoupled from one another the shock absorber is relieved fromapplying a dampening force to the seat.

In accordance with a further aspect of an embodiment, the first membermay comprise a housing with an interior and an exterior with the shockabsorber being substantially positioned or disposed within the interiorof the housing and thereby protected by the housing. In addition, thelatch may also be carried by the housing and operated by a latchactuator to selectively couple and decouple the shock absorber to andfrom the housing to thereby selectively apply and relieve theapplication of the dampening force to the seat. The latch actuator maybe a fluid actuator, such as a pneumatic actuator, an electricallyoperated actuator, such as a motor, for shifting the latch to couple anddecouple the shock absorber in response to the actuator. Although lesspreferred, a mechanical actuator may be used of the type which ismanually shifted to couple and decouple the shock absorber to and fromthe housing.

As another aspect of an embodiment, the shock absorber may include acylinder or exterior housing with a latch gripping surface carried bythe cylinder. The latch gripping surface may be a friction enhancedsurface or may comprise a mechanism mounted to the cylinder such as aplurality of teeth. The shock absorber also may include a dampeningpiston within the cylinder and a piston rod coupled to the piston andhaving an end portion projecting outwardly from the piston for couplingto the other of the vehicle and seat (the other of the vehicle and seatin this case being the other of these components to which the firstmember or housing is not coupled).

The latch may include at least one latch arm with a latch surface whichmay be a friction enhanced surface. Like the latch gripping surface, thelatch surface may comprise a plurality of teeth. The latch arm may becoupled to the first member or housing with the latch arm being movablebetween first and second positions. When the latch arm is in the firstposition, the latch surface of the latch arm engages the latch grippingsurface carried by the cylinder to thereby couple the shock absorber tothe first member or housing. When the latch arm is in the secondposition, the latch surface is disengaged from the latch grippingsurface. The latch arm may be pivoted to the first member or housing, inthe case wherein the first member takes the form of a housing, forpivoting movement between the first and second positions. In onespecific approach, both the first member, such as the housing, and latcharm are pivotally coupled to said one of the vehicle and seat forpivoting about a common first pivot axis.

As another aspect of an illustrated embodiment, the shock absorbercylinder may be slidably coupled to the first member, or housing in thecase the first member takes the form of a housing, for sliding movementrelative to the first member. Thus, the first member may comprise ahousing having a first side wall with an exterior surface at theexterior of the housing and an interior surface at the interior of thehousing. The first side wall may include first and second side wallportions spaced apart from one another to define a guide slottherebetween. The slide element may be mounted to the cylinder andslidably coupled to the first and second side wall portions such thatthe slide element slides along the guide slot and guides the slidingmotion of the cylinder and thereby the shock absorber relative to thehousing. This sliding inter-connection of these elements may beindependent of the operation of the latch.

In a more specific approach, the cylinder may be substantially disposedwithin the housing. In addition, the slide elements may include firstand second inter-connected slide members which sandwich the respectivefirst and second side wall portions therebetween. In this case, thefirst slide member may be positioned substantially within the housingand may include respective first and second teeth containing flangeportions extending in a direction away from the first side wall of thehousing, the first and second teeth containing flange portions beingspaced apart from one another and positioned at opposite sides of thecenter of the cylinder from one another. Furthermore, the latch arm mayhave a generally U-shaped cross-section with a base and first and secondleg portions. The first and second leg portions may each terminate in anelongated row of teeth and are aligned with a respective adjacent one ofthe first and second teeth supported flange portions of the first slidemember. The teeth of the first and second leg portions engage the teethof the respective adjacent flange portions when the latch arm is in thefirst position.

As a further aspect of an embodiment, the housing may include a secondwall opposite to the first wall, the second wall including an arm flangereceiving opening therein. The latch arm includes an arm flangeprojecting outwardly from the base toward the arm flange receivingopening. An actuator guide flange also projects outwardly from thesecond wall of the housing with the guide flange defining the actuatorguide slot. A fluid actuator is provided for operating the latch, theactuator having an actuator cylinder which is pivoted to the housing, anactuator piston within the actuator cylinder, and an actuator pistonrod. The actuator piston rod has an end portion projecting outwardlyfrom the actuator cylinder. A link pivotally couples the end portion ofthe actuator piston rod to the latch arm flange. The end portion of theactuator piston rod is also coupled to the actuator guide flange suchthat the actuator guide slot guides the movement of the actuator pistonrod during extension and retraction of the actuator piston rod. In thisexample, extension of the actuator piston rod shifts the latch arm tothe first position and retraction of the actuator piston rod shifts thelatch arm to the second position.

As yet another aspect of an embodiment, the shock absorber may beadapted to provide a non-linear dampening force to the seat to dampenseat vibrations. For example, the dampening force may be constant for afirst range of movement of the seat in response to vibrations from ahome position of the dampening piston and increasing for certainmovements of the dampening piston in excess of the first range ofmovement.

In accordance with another embodiment, first and second latch arms arepivoted to the housing and are disposed at opposite sides of a cylinderdisposed substantially within the housing. These latch arms each have acentral portion and first and second end portions. The latch arms eachpivot about an axis through a central portion of the latch arm. Thefirst end portion of each latch arm includes a latch surface and thecylinder has an exterior with an elongated latch gripping surface. Afluid actuator is coupled to the second end of each of the arms byrespective links. Extension and retraction of the fluid actuator, andmore particularly of an actuator piston rod, is translated through thelinks into pivoting motion of the first and second latch arms betweenrespective first positions in which latch surfaces of the latch armsengage the latch gripping surfaces of the cylinder and second positionsin which the latch surface and latch gripping surfaces are disengaged.

The present invention is directed toward novel and non-obvious featuresof a vibration dampener, both individually and collectively, as setforth above and as additionally set forth in the drawings anddescription which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially broken away perspective view of one embodiment ofa seat suspension system in accordance with the present invention in apartially elevated state.

FIG. 2 is a side elevation view of the seat suspension system of FIG. 1in a lowered position relative to FIG. 1 and illustrating a portion of aseat supported by the seat suspension system.

FIG. 3 is an exploded view of the seat suspension system similar to thesystem of FIG. 1.

FIG. 3A is a schematic illustration of one form of a seat supportillustrating several specific pivot axis points for link members used inthis support relative to an X-Y axis coordinate system.

FIG. 3B is a schematic illustration like that shown in FIG. 3A, but alsoshowing a seat occupant and the path of travel of selected portions ofthe body of the seat occupant in response to vibrations, with the pivotaxis points shown in FIG. 3B like those shown in FIG. 3A.

FIG. 3C is similar to FIG. 3B except that the pivot axis points arelocated at different coordinates, this figure showing the effect ofadjusting the coordinates on the motion of various body parts of theseat occupant.

FIG. 3D is like FIG. 3C with the pivot axis points at a location whichdefines a true parallelogram.

FIG. 4 is a perspective view of one form of vibration damper usable inthe embodiment of FIG. 1 looking generally toward the front of thevibration damper.

FIGS. 5 and 6 are side elevation views of the vibration damper of FIG.4, showing the vibration damper in respective latched and unlatchedpositions.

FIG. 7 is a top view of the vibration damper of FIG. 4.

FIG. 8 is a rear elevation view of the vibration damper of FIG. 4.

FIG. 9 is a partially exploded view of an alternative form of vibrationdamper usable in the embodiment of FIG. 1.

FIG. 10 is a vertical sectional view through one form of vibrationdampening cylinder for the vibration dampers of FIGS. 4 and 9.

FIG. 10A is a graph illustrating an example of the non-linear dampeningforce which may be applied by the dampening cylinder of FIG. 10.

FIG. 10B is a graph illustrating an example of the dampening forceversus displacement from a home position in response to shifting thepiston of a shock absorbing damper of FIG. 10 at a velocity which variessinusoidally.

FIG. 11 is a perspective view of an alternative embodiment of a seatsuspension system in accordance with the invention.

FIG. 12 is a side elevation view, partially in section, of the seatsuspension system of FIG. 10, shown with a seat in a partially elevatedposition and also showing a latch in a latched state.

FIG. 13 illustrates a portion of the seat suspension system of FIG. 11with the latch shown in an unlatched state.

FIG. 14 illustrates an alternative form of vibration dampening cylinderfor the seat suspension systems of FIGS. 1 and 11.

FIG. 15 is a side elevation view of a seat suspension system includingan alternative form of latch.

FIG. 16 is an enlarged vertical sectional view of the latch used in theembodiment of FIG. 15 with the latch shown in a latched state.

FIG. 16A is a cross-sectional view of the latch of FIG. 16 taken in thedirection of arrows 16 a—16 a and illustrating the operation of thelatch to grip a rod passing through the latch.

FIG. 17 is a vertical sectional view through the latch of FIG. 15showing the latch in an unlatched position to permit the passage of therod through the latch.

FIG. 17A is a vertical sectional view through an alternative latchsimilar to that shown in FIGS. 16, 16A and 17.

FIG. 18 schematically illustrates an alternative embodiment of a seatsuspension system in accordance with the present invention.

FIG. 19 schematically illustrates one form of control circuit for theillustrated seat suspension embodiments.

FIG. 20 illustrates an exemplary pneumatic circuit usable in theillustrated forms of seat suspension systems.

FIGS. 21A-21C schematically illustrates a valve which may be utilized tocontrol both seat elevation adjustment and the operation of a latch.

FIGS. 22A, 22B, 22C, 22D and 22E illustrate in greater detail onesuitable valve actuated by a single lever for simultaneously causing theunlatching of a latch and seat height adjustment.

DETAILED DESCRIPTION

FIGS. 1-3 illustrate one form of a seat suspension system 10 forsupporting a seat 12 (a portion of which is shown in FIG. 2) for raisingand lowering the seat in elevation relative to a floor 14 of a vehiclewithin which the seat suspension system is positioned. For example, theseat suspension system 10 may be mounted to the floor of a truck. Insuch a case, vibrations imparted to the truck during travel over a roadsurface can cause some vibration of the floor 14 and also of thesupported seat 12. Consequently, it is desirable in such applications todampen the road vibrations.

The illustrated seat suspension system 10 includes a seat support, oneform of which is generally indicated at 20, which is raisable andlowerable to support the seat at various elevations relative to thefloor 14 of the vehicle. The illustrated seat support includes a seatsupporting member 22 to which the seat 12 is mounted (FIG. 2). First andsecond link elements 24, 26 are pivotally connected at their upper endportions to the support member 22 and at their lower end portions to abase member 30. More specifically, link member 24 is pivoted at itsupper end portion to support member 22 for pivoting about a first pivotaxis 32 extending transversely through the seat support member. Inaddition, the lower end portion of link member 24 is pivoted to the base30 for pivoting movement about a transverse axis 34 which is parallel tothe axis 32. In addition, link member 26, which in the illustrated formis positioned below link member 24, has an upper end portion pivoted tothe seat support member 22 for pivoting about a transverse axis 36. Thelink member 26 also has a lower end portion pivoted to the base 30 forpivotal movement about an axis 38. Axes 32, 34, 36 and 38 in theillustrated form are parallel to one another. Consequently, aparallelogram type support is provided for the seat member 22. The axes32-36 may be positioned such that a line through axes 32, 34 is parallelto a line through axes 15 36, 38 in a true parallelogram support.However, the axes 32-38 may be positioned such that the line throughaxes 32, 34 is not parallel to the line through axes 36,38;

for example, to control seat motion as explained below in connectionwith FIGS. 3A-3D.

Base 30 is adapted for mounting to the floor 14 of the vehicle. Forexample, a plurality of fastener receiving openings, one being indicatedat 40, are provided for receiving fasteners which secure the base 30 inplace. Alternatively, base 30 may be eliminated with link members 24, 26being pivoted directly to the floor or other vehicle supports. Also, thebase 30 may be adapted for mounting to a wall surface of a vehicleinstead of the floor 14. Nevertheless, the illustrated seat support isadvantageous because the floor of the vehicle provides stable supportfor the seat support 20 and the seat support can be installed as amodular unit.

As best seen in FIG. 3, the illustrated base 30 includes first andsecond upright side elements 60, 62 interconnected by front and reartransverse cross-piece elements 64, 66. Openings are provided in therespective side elements 60, 62 for receiving 30 pivot pins 70, 72 whichpivot the lower end portions of the respective link members 24, 26 tothe base 30 for pivoting about axes 34 and 38. To reduce the weight ofthe overall construction, the upright elements 60, 62 may be of agenerally hollow construction with a plurality of reinforcing ribs, someof which are indicated at 78, and a perimeter flange 79 being providedfor reinforcing these elements and also the openings through which thepins 70, 72 extend. The central region of base 30 may also be providedwith a void 80 for further weight reduction purposes. In addition, asexplained more fully below, the base 30 may include upright vibrationdamper supporting bracket elements 82, 84 to which a vibration damper200 is interconnected, such as by pivot pins 86, 88. The axis throughpins 86 and 88 in the illustrated embodiment is parallel to the axesthrough the pins 70, 72. The pins 70, 72 may, as shown in FIG. 1,comprise four short pins instead of longer pins transversing the widthof the base

Although other materials may be used, typically the base 80 is of castmetal such as aluminum. Plastics and other durable materials mayalternatively be used for the base. The base may also be of fabricatedsheet steel. In addition, the base may take other forms.

The support member 22 shown in FIGS. 1-3 includes first and secondupright side flanges 90, 92 having respective elongated spaced-apartplanar seat mounting surfaces 94, 96, which are generally parallel toone another. The mounting surfaces include plural fastener receivingopenings, some being indicated at 98 in FIG. 1, for use in mounting theseat 12 to the seat support member 22. Like base side components 60, 62,the seat support side components 90, 92 may be generally hollow with aplurality of reinforcing ribs, some being indicated at 100 in FIG. 1,and a perimeter flange 101 or lip for reinforcing the side elements andthe pivot axis defining openings. Pins 103, 105 (FIG. 3) pivot therespective upper end portions of link members 24, 26 to the seat supportmember 22. As shown in FIG. 1, four such pins may be used, one at eachcorner of the interconnected seat support 20. Also, front and rear crosscomponents 102, 104 are provided to interconnect the side flanges 90,92. A central platform 108 may also be provided between these twoflanges. Voids 110, 112 between these cross pieces further reduce theweight of the illustrated seat supporting member 22. The cross pieces102, 104 may include appropriate reinforcing ribs as shown. Like base30, the seat support member 22 may be of a durable material and may becast of steel. Thus, base 30 and seat support member 22 may each be of amonolithic one-piece homogenous unitary cast structure.

The seat support member 22 may be eliminated with elements such as linkmembers 24, 26 being connected directly to the seat. In such a case, theseat 12 would typically be rigidified at its base. However, by makingseat support 20 a combination of base 30, links 24 and 26 and an upperseat support member 22, a modular construction results as the seat canbe separately manufactured and installed to the seat support member 22at a later time.

The link member 24 may include first and second side elements 130, 132with transverse cross-piece portions 136 (one of which is shown in FIG.1). These elements together form a platform-like, generally rectangularlink member. For weight reduction purposes, the link member may begenerally hollow with reinforcing ribs such as indicated at 138 in FIG.1 and interior and exterior flanges 140, 141. Flange 140 may bound anenlarged opening 143 through the link member 34 for accommodating thevibration dampener 200, as explained below. The lower link member 26 maybe similarly constructed with side elements 142, 144 and transversecross-piece portions, one of which is shown at 146 in FIG. 1. The linkmember 26 may also be generally hollow with reinforcing ribs (some beingindicated at 147) extending between interior and exterior flanges 148,149. The central portion of link member 26 is generally hollow, althoughthe illustrated link member 26 has a central cross-piece such asplatform 150 for supporting an air spring as explained below.

As can be seen in FIG. 1, the base side members 60, 62 may be taperedwith an increasing height from front to rear of the seat support 20.Also, pivot axis 34 may be positioned rearwardly and above pivot axis38. Similarly, the side elements 90, 92 of seat support member 22 may bereduced in height from front to rear of the seat support 22 and may alsoaccommodate a pivot axis 32 positioned above and rearwardly of the pivotaxis 36. Consequently, as the seat support is pivoted downwardly (shownmoving from FIG. 1 to FIG. 2), the seat support member 22 shiftsprimarily downwardly with the surfaces 94, 96 remaining substantiallylevel. Conversely, when the seat support is raised (moving from FIG. 2to FIG. 1), the seat supporting surfaces 94, 96, and thereby the seat12, moves primarily upwardly, with the seat remaining substantiallylevel.

The link members 24, 26 may take different forms. For example, the linkmembers 24 and 26 in FIG. 3 are of a somewhat different structure, withcorresponding elements being assigned the same numbers., Thisillustrates the fact that the structure of link elements 24, 26 may bevaried, with an alternative form being shown in FIG. 3. The link members24, 16 may also, for example, comprise individual spaced-apart arms atopposite sides of the seat. The seat support 20 may also take a varietyof forms, although the form illustrated in FIGS. 1-3 offers a number ofadvantages. For example, a scissors-type seat support mechanism may beused, as well as other seat supports capable of raising and lowering theseat.

With reference to FIGS. 3A-3D, and with a number of the components ofthe seat support system, such as a seat height adjuster and latch (ifused) eliminated for convenience, first and second link members 24, 26are shown pivotally coupled at their lower end portions to base 30 andat their upper end portions to seat supporting member 22. The centers ofthe pivots 38, 36 are indicated respectively by the numbers 1 and 2, andthus correspond to the pivot axes through pivots 38 and 36. Similarly,the centers of the pivots 34, 32 are indicated respectively by thenumbers 3 and 4, which thus correspond to the pivot axes through pivots34, 32. For convenience in this description, the first pivot axis thuscorresponds to number 1, the second pivot axis thus corresponds tonumber 2, the third pivot axis thus corresponds to number 3, and thefourth pivot axis thus corresponds to number 4.

In these figures, an X-Y coordinate system is indicated, with the X axisbeing horizontal and in this case parallel to the illustrated floor 14.In addition, the Y axis of this coordinate system is vertical. Thecoordinate system is located so that both the X and Y axes intersectfirst pivot 1 and thus first pivot 1 has coordinates (0, 0) in this X-Ycoordinate system.

As the links 24, 26 are pivoted clockwise in FIG. 3A, the seat 12 israised. Conversely, when the links are pivoted counter-clockwise in FIG.3A, the seat 12 is lowered. In these figures, the seat support is shownwith the line segment L extending from the first pivot 1 to the secondpivot 2 and at an axle of θ relative to the X axis, with θ being 20.3degrees. Obviously, the angle θ changes as the arms 24, 26 are pivotedto new locations. In FIG. 3A, the line segment R extends from the thirdpivot 3 to the fourth pivot 4, the line segment B extends from the firstpivot 1 to the third pivot 3, and the line segment S extends from thesecond pivot 2 to the fourth pivot 4.

In the construction illustrated in FIG. 3A, the links 24, 26 are ofunequal length. That is, the length or distance R between the third andfourth pivots 3, 4 is different from the length or distance L betweenthe first and second pivots 1, 2. More specifically, the distance R isgreater than the distance L. Consequently, the FIG. 3A constructioncomprises an unequal arm length parallelogram type support. In aspecific embodiment, the distance R is from about twelve percent toabout twenty percent greater than the distance L and assists incontrolling the motion of the seat. Assume the pivot 3 is shifted to thelocation indicated by 3′ and thus segment R is shifted to R′. In thislatter case, R′ is equal to L in length and R′ is parallel to L,providing a true parallelogram support. Although this can be done, asexplained below the resulting motion of selected portions of a seatoccupant's body have greater horizontal components of motion than if theillustrated FIG. 3A unequal parallel arm support is used.

Again referring to FIG. 3A, in this illustrated construction, the thirdpivot axis 3 is at an elevation which is above the elevation of firstpivot axis 1. Also, in this illustrated construction, the fourth pivotaxis 4 is positioned above and rearwardly of the second pivot axis 2.When the seat of this figure is in a raised position, the first andsecond link members 24, 26 are angled forwardly and upwardly relative tothe floor of the vehicle. Furthermore, with the constructions shown inFIGS. 3B and 3C, the absolute value of the slope of line L relative tohorizontal is greater than or equal to the absolute value of the slopeof line R relative to horizontal when the seat is supported in variousraised positions. Also, a plane extending upwardly through third andfourth pivots 3, 4 intersects a plane extending upwardly through firstand second pivots 1,2 at a location which is above the floor of thevehicle when the seat is raised.

The pivot axes may be located relative to one another according to theformula L<(S+R−B). In this formula, L is the distance between the firstand second pivot axes, S is the distance between the second and fourthpivot axes, R is the distance between the third and fourth pivot axes,and B is the distance between the first and third pivot axes.

In the specific example shown in FIGS. 3A and 3B, and with θ at 20.3degrees, the coordinates of pivot 1, as previously mentioned, are (0, 0)on the illustrated X-Y coordinate system; the coordinates of pivot 2 inmillimeters are (−347.7, 128.5); the coordinates of pivot 3 are (259.6,42.5); and the coordinates of pivot 4 are (−165.4, 177.8).

The location of these pivots in this illustrated embodiment may beselected such that the movement of a selected portion of a seatoccupant's body in response to seat vibrations is confined to movementin a substantially vertical direction. For example, as best seen in FIG.3B, with the specific coordinates set forth above, movement of variousbody points of a seat occupant 169 are shown. Specifically, with theseat at a selected elevation corresponding to the given θ and occupant169 sitting on the seat and the seat being stationary, the position ofthe occupant's hip point 171, shoulder point 173, and eye point 175 areshown. For reference purposes, vertical line segments 177, 179 and 181are shown passing through the respective hip point 171, shoulder point173, and eye point 175. In response to seat vibrations, as explainedbelow, the seat may move both upwardly and downwardly from the staticposition. Correspondingly, the respective hip point 171, shoulder point173, and eye point 175, also move upwardly and downwardly. The X's shownadjacent line 177 indicate points through which the hip point 171 passesas it moves upwardly and downwardly in response to vibrations.Similarly, the X's adjacent to line 179 indicate the path followed bythe shoulder point 173 as the seat moves upwardly and downwardly.Finally, the X's adjacent to line 181 indicate the path followed by eyepoint 175 as the seat moves in response to vibrations.

In FIG. 3B, the shoulder point 173 travels more closely along a verticalline than either the eye point or hip point. That is, the shoulder pointis confined to move in a substantially vertical direction.

More specifically, assume that the total range of movement in responseto vibration between the lower extreme and the upper extreme is calledthe suspension stroke. By substantially vertical motion, it is meantmotion having a horizontal component which is no more than about sevenpercent of the length of the suspension stroke from vertical. Forexample, in FIG. 3B, with the pivots having the coordinates shown andwith the suspension stroke (the total vertical motion of the seat inresponse to vibration) being 165 mm, the maximum deviation of hip point173 from vertical line 179 is about 6.6 mm, or about four percent of thesuspension stroke.

Since very little off-vertical motion occurs at this location, lessundesirable rubbing of a three-point shoulder strap on the occupant'sshoulder at this location takes place. Also, for occupant's prone totravel sickness, it is desirable to have less elliptical or off verticalmovement of the stomach and inner ear of such occupants. By confiningthe shoulder to substantially vertical movement, a compromise isachieved. That is, the inner ear more closely moves in a verticaldirection than would be the case if seat pivot locations were optimizedto confine the motion of the stomach to a substantially verticaldirection. In addition, the stomach moves more vertically than would bethe case if the pivot locations were optimized to confine movement ofthe eye or inner ear of the occupant to substantially vertical movement.

FIG. 3C illustrates an example where the pivot axis points 1-4 areselected to minimize the horizontal component of movement of the eyepoint 175 of the seat occupant 169. As can be seen in FIG. 3C, theshoulder point 173 has greater horizontal components of movement thanthe horizontal components of movement of shoulder point 173 in the casewhere the pivot axis points 1-4 are positioned as shown in FIG. 3B. Morespecifically, in FIG. 3C, θ again is at 20.3 degrees. In addition, thecoordinates of pivot 1 are (0, 0); the coordinates of pivot 2 are(−364.8, 35.9); the coordinates of pivot 3 are (259.6, 42.5); and thecoordinates of pivot four are (182.3, 49.2). With these specificexemplary coordinates, the maximum deviation of eye point 175 fromvertical line 181 is 10 mm, or about six percent of the entire 165 mmsuspension stroke.

In these examples, the vertical lines 179, 181 are located to intersectthe respective shoulder point 173 and eye point 175 when the seat is inthe static position supporting an occupant with no seat vibration. Thus,the phrase “substantially vertical motion” is defined to mean motion ofno more than about ten percent and most preferably no more than sevenpercent from vertical over the entire suspension stroke.

In comparison, FIG. 3D shows the seat support with the third pivot at 3′to provide a true parallelogram support. In the FIG. 3D example, with θagain equal to 20.3 degrees, the coordinates of the pivots inmillimeters are as follows: pivot 1 at (0, 0); pivot 2 at (−347.4,128.5); the third pivot 3′ at (182.3, 49.2); and the fourth pivot at(−165.4, 177.8). In this case, with a suspension stroke of 165 mm ofvertical motion, the shoulder point (as well as the hip and eye points)have a maximum deviation which is understood to be about 48.5 mm (abouttwenty-nine percent) from vertical.

Thus, the modified unequal parallelogram supports of FIGS. 3B and 3C areexamples illustrating the selection of pivot axis locations to confineselected portions of an occupant's body to a more vertical direction.Moreover, it should be noted that the vertical motion achieved by theshoulder point in the FIG. 3B example does not deviate significantlyfrom precise vertical motion of the shoulder achieved with someconventional scissors style seat supports.

It should be noted that the locations of pivots 32-36 may be varied. Inaddition, as previously mentioned, in some embodiments of a seatsuspension system, the modified or true parallelogram type support maybe replaced with scissors or other types of support mechanisms.

A seat height adjuster is used to raise and lower the seat 12 betweenvarious elevations relative to the floor 14 and to a selected elevation.In general, a mechanism may be employed which moves seat support 22 oreither of the link members 24, 26 about their respective pivots. Thesemechanisms may, for example, comprise hydraulic or pneumatic activatedscrew jacks or other mechanisms. As a specific example, an air spring170 (see FIGS. 1 and 3) may be used for this purpose. The illustratedair spring may, for example, be from the “Airide Springs” product linefrom Firestone of Carmel, Calif. The illustrated air spring 170 issupported on the platform 150 of link member 26 beneath the seat supportmember 22 and engages the undersurface of platform 108 of member 22.Upon inflation of air spring 170, the seat support member 22 and seat 12is shifted upwardly. In contrast, upon deflation of air spring 170, theseat support member 22, and thereby the supported seat 12, shiftsdownwardly. A seat height controller may be used to control the airpressure delivered to and removed from the air spring 170 to therebyadjust the height of the seat to a selected elevation. The seat heightis adjustable by the seat height adjuster between an uppermost elevationand a lowermost elevation which is established by the mechanical limitsof the seat suspension system 10. For example, although variable, theseat may be adjustable in elevation from a lowest position whichpositions the hip point 437 mm above the floor 14 to a highest hip pointposition which is 537 mm above the floor, for a total elevationadjustment of 100 mm (about four inches. The term “hip point” refers tothe location where a typical driver's hip joint is positioned when thedriver is seated in the seat. The seat height adjuster, such as airspring 170, allows the supported seat to move in response to vibrations,for example from the road surface. This provides for a more comfortableride.

The vibration dampener 200 is provided to dampen the vibrations of theseat. In the form illustrated in FIGS. 1-3, the vibration dampenerincludes a shock absorber or dampening cylinder 201 with an externalhousing 202 and a dampening piston therein (one example being describedbelow in connection with FIG. 10). The dampening piston is coupled to apiston rod 206. The piston rod may be of circular cross-section or ofany other cross-section. For example, FIGS. 3-9 show a shaft 206 havinga square cross-section. The lower end portion of the vibration dampener200 is, in the illustrated embodiment, pivoted to the respectiveelements 82, 84 of base 30 rearwardly of pivot 38. The upper end portionof the vibration dampener in this form, and in particular the upper endof rod 206, is pivoted at 210 (FIG. 1) rearwardly of pivot 32 andbetween respective ear flanges 212, 214 which project rearwardly fromcross-piece portion 104 of the seat support member 22. The dampeningpiston is biased towards a first or home position such that thevibration dampener, when engaged to the seat support 20, dampensmovements of the dampening piston away from the home position to therebydampen corresponding vibrations of the seat 12. In this specificembodiment, the dampening cylinder is supported for selective movementrelative to the floor 14 of the vehicle. Consequently, the elevation ofthe first or home position is adjustable to correspond to adjustments inthe selected elevation of the seat. More specifically, in thisillustrated form, each time the seat height adjuster operates to adjustthe height of the seat, the elevation of the dampening cylinder andthereby of the home position is adjusted. More specifically, theillustrated seat height adjuster and vibration damper cooperate toautomatically and simultaneously adjust the elevation of the firstposition of the dampener with changes in the selected elevation of theseat.

The illustrated vibration dampener 200 includes a latch mechanism 220which selectively engages and releases the dampening cylinder 201. Whenreleased, the dampening cylinder 201 is free to move relative to thelatch. That is, as the seat is raised, the dampening cylinder 201,because it is coupled to seat member 22 at the upper end of rod 206, israised the same distance as the seat. Consequently, the home position ofthe dampening piston within the housing 202 remains at a constantlocation within the cylinder, yet the elevation of the home positionchanges with the changes in elevation of the cylinder 201.

Once the seat height is at a desired elevation, the latch mechanism 220may be operated to re-engage the dampening cylinder 201. Whenre-engaged, the cylinder is in a fixed position relative to the seatsupport 20 and the dampening cylinder applies a dampening force to theseat. That is, vibrations in the seat cause corresponding vibrations inrod 206 which are dampened by the movement of the dampening pistonwithin the cylinder 202. Other ways of adjusting the elevation of thehome position may also be used. For example, the cylinder may besupported by a jack or other mechanism which raises the cylinder anamount which corresponds to the change in seat elevation withoutdecoupling the cylinder. Various forms of latch mechanisms 220 may alsobe used, some specific examples of which are explained in greaterdetail, below.

The latch 220 may be operated to release the dampening cylinder duringthe entire time the seat height is adjusted or only during portions ofsuch time. The vibration dampener is thus adapted to selectively relieveand apply a dampening force in these embodiments in which the dampeningcylinder is latched and released. Furthermore, with this approach, theposition within the vibration dampening cylinder 201 need not extend andretract over the entire range of seat height adjustment controlled bythe air spring, 170 or other seat height adjuster. In a specificexample, the dampening cylinder 201 may be designed to allow movement ofthe dampening piston a total of about sixty-five millimeters (about 2.5inches). Although this may be varied, this compares to a total seatheight adjustment in this example of about 100 mm (about four inches).Furthermore, a vibration dampener may be used which applies a variabledampening force to seat vibrations, including a dampening force whichvaries non-linearly with the magnitude of seat movements in response tovibrations. For example, the applied dampening force may be higher for amore extreme movement in response to seat vibration than applied in thecase of a lesser movement in response to seat vibration and may bevaried non-linearly for such movements between such movements. Morespecifically, the applied dampening force may be constant for limitedmotions from a home position and increase with more extremes in motionfrom the home position. This is facilitated by a design in which thehome position of the dampener is shifted with changes in elevation ofthe seat.

Assume the seat has been moved to an elevation which is three incheshigher than the previous elevation to an elevation which is twelveinches above the floor of the vehicle. With the illustrated design, thehome position of the dampening cylinder may also be shifted threeinches. If the seat then moves downwardly a certain amount (for example,thirty millimeters), in response to a seat vibration, a first dampeningforce may be applied to such motion. If thereafter the seat movesdownwardly thirty-five millimeters from the home position, a greaterdampening force may be applied. The dampening force may be variednon-linearly with deviations from the home position. Upward changes inseat elevation in response to vibrations can be dampened in a similarmanner. If the home position had not been changed, the seat ride wouldno longer be the same, at least for given movements in response tovibration if a non-linear dampening force were being applied. That is,in this specific example, if the home position remained fixed and theseat elevation had been raised three inches, a further upward movement(e.g. one-half inch) in elevation of the seat in response to a vibrationwould now make the seat three and one-half inches from the homeposition. If a non-linear dampening force were being applied, this forcewould differ from the force being applied if the seat had not beenraised and the seat were influenced by the same vibration, as in thiscase the seat would only be one-half inch from the home position. Thus,the illustrated seat suspension system facilitates the use of anon-linear dampening force. Furthermore, this type of seat suspension 10permits the application of substantially the same dampening forceimmediately after a height adjustment as the dampening force providedimmediately before the height adjustment.

The seat suspension system 10 of FIGS. 1-3 also includes an optionalseat leveling feature. In operation, if the load on the seat is varied,for example, by an occupant getting up from the seat, the air spring 170will tend to expand in response to this reduced load. As a result, seatsupport 22 is raised and also the supported seat 12. If the particularseat happens to be the driver's seat, the upper surface of the seat mayengage or come very close to the undersurface of the vehicle steeringwheel. When the driver returns and again sits on the seat, it can bedifficult for the driver to fit his or her legs between the steeringwheel and seat until after the driver's weight has been placed on theseat to again compress the air spring to move the seat back to itsoriginal position. In the illustrated embodiment, a seat position sensormay be used to detect motions of the seat which are outside the range ofmotions being dampened by the dampener. In response to detection of suchout of range motion, the inflation of the air spring 170 is adjusted toreturn the seat toward the position it was in before the motion tookplace. In other words, when the driver leaves the seat and the seatrises, pressure on the air spring is relieved to bring the seat backtoward the position it was in prior to the driver leaving the seat.Conversely, when the driver again sits on the seat and the seat tends todepress outside of normal dampening ranges, the air spring is inflatedto again return the seat toward its home position.

In one illustrated form, the position sensor comprises a self-levelingvalve 230 coupled by a link 232 to the vibration dampener 200. Morespecifically, the link 232 is coupled to a bracket 234 connected to thedampening cylinder 202. The link 232 is 10 slidably coupled to the valvestem of valve 230 to accommodate variations in the distance between thevalve stem and bracket 234 during operation of the illustrated system.The illustrated valve 230 is a rotary leveling valve and has a dead zonecorresponding to the movements by the seat in response to vibrationswhich do not result in self-leveling. For example, assume movements oftwenty-five millimeters or less in extension and forty millimeters orless in compression of the dampening cylinder are dampened by thedampening cylinder. Most movements in response to vibration involve lessthan 10 mm in extension and 10 mm of compression. In some observations,over ninety percent (90%) of extensions and over ninety percent (90%) ofcompression were within this range. Thus, although variable, the deadzone may be set to permit movements of 10 mm extension and 10 mmcompression. It is expected that movements in compression will deviatemore from the home position. Thus, the dead zone in compression may begreater than the dead zone in extension, with 15 mm compression being aspecific example. Once the dead zone motion is exceeded, this motioncauses link 232 to operate the valve to commence inflation of the airspring 170 and raise the seat if the seat elevation has dropped belowthe dampening range. Conversely, the valve is operated to commencedeflation of the air spring 170 to lower the seat in the event the seatelevation is raised beyond the range of motion being dampened. Althoughtimers or other delays may be used to only respond to deviations of asignificant duration, this option may be eliminated. Consequently, amomentary deviation outside the dead zone is minimized because littlechange in air spring inflation occurs during any such momentarydeviation. As a specific example, valve 230 may be a Model 3107-1leveling valve from GT Development of Seattle, Wash. Other positiondetection sensors such as from Wabco, Inc. or other sources may be used,although the illustrated approach is convenient and mechanically simple.When latch 220 is unlatched and the dampening cylinder is shifted fromone position to the other in response to changes in the elevation of theseat, the link 232 shifts with the dampening cylinder and remains in thesame relative position to the valve 230. Consequently, the valve 230 inthe illustrated approach does not operate when the seat elevation isdeliberately being adjusted by the air spring 170.

One form of suitable vibration dampening module 200 utilized in theembodiments of FIGS. 1-3 is illustrated and described below inconnection with FIGS. 4-8. This form of vibration dampener 200 includesan outer housing 300 having pivot receiving openings 302, 304 throughwhich pivot pins are inserted to pivot the housing to the respectiveears 82, 84 of base 30 (FIG. 1). Consequently, the housing 300 (FIGS.4-8) is free to pivot about an axis 306 and relative to the base member30. The housing 300 may include cut-outs, such as indicated at 308 (FIG.4) for weight reduction purposes. In addition, the housing 300 maydefine a guide slot 310 extending along the full length of one side wall312 of the housing. The side wall 312 of the illustrated housingincludes respective flanges 314, 316 which extend inwardly toward oneanother and define the guide slot 310 therebetween. The illustratedhousing is generally rectangular in cross-section with a side wall 320opposing side wall 312 and side walls 322, 324 interconnecting the sidewalls 320 and 312. The housing 300 may be stamped or otherwise formedfrom a durable material, with steel being a specific example.

A latch arm element 330 is pivoted to housing 300, for example by thesame pivots which couple the housing to the base 30, so that the latcharm element 330 may pivot relative to the base.

As best seen in FIG. 7, latch arm element 330 may be generally U-shapedin cross-section, having a base portion 332 and first and second legportions 334, 336. A latch actuator engaging flange 338 extendsrearwardly from base 332 and, in this case, through an opening 340 (seeFIGS. 5 and 6) through the wall 320. Each of the elements 334, 336includes a respective latch surface 344, 346 which may comprise afriction enhanced surface. In the form shown in FIGS. 5 and 6, the latchsurfaces comprise an elongated row of teeth 350. The latch 330 isselectively operable to couple and decouple the dampening cylinderhousing 202 to the housing 300 and thus the dampening cylinder 201 tothe base 30 (FIG. 1). More specifically, the cylinder housing 202 (FIGS.4-8) includes a latch gripping surface which may be a friction enhancedsurface which is selectively engaged by the latch 330. The latchgripping surface may be, as illustrated, provided by one or moremembers, such as a plate 360 (FIGS. 4-7) welded or otherwise secured tothe exterior housing 202 of the cylinder 201. The plate 360 (see FIG. 7)includes first and second outwardly projecting side legs 362, 364. Theleg 362 extends outwardly toward side wall 324 and turns inwardly alongthe interior of the wall 324 to extend toward wall 320. The distal edge366 of leg 360 comprises a friction enhanced latch gripping surface,such as an elongated row of teeth which are selectively engaged ordisengaged by the corresponding teeth 350 of the latch 330. Similarly,leg 364 extends outwardly toward the wall 322 and then turns to extendalong the interior of wall 322 toward the wall 320. The leg 364terminates at its distal edge provided with a latch gripping surface 368which may also comprise a row of gripping teeth. A backup plate 370 isconnected to the cylinder 202 and, more specifically, this connection ismade through the plate 360. Backup plate 370 may include side flanges372, 374 which are spaced from the respective legs 362, 364 as shown inFIG. 7 to receive the wall portions 314, 316 of the wall 312therebetween. Consequently, when latch 330 is released to free grippingsurfaces 366, 368 from surfaces 344, 346, the cylinder may sliderelative to housing 300. In this case, the movement of the cylinderguided by flanges 314, 316.

Referring to FIGS. 5 and 6, the illustrated vibration dampener 200includes a latch actuator such as a pneumatic cylinder 390 having aninternal piston (not shown) coupled to a piston rod 392.

A link 400 is pivoted to the distal end 402 of the rod and also at 404to the flange 238. The distal end of the piston rod is also coupled tothe housing 300 so that motion of the piston rod is guided. Morespecifically, as best seen in FIGS. 5 and 6, an elongated, generallyupright slot 406 is provided in a flange 408 projecting rearwardly fromhousing 300. The pin which couples link 400 to the distal end of rod 392at location 402 may also extend through the slot 406 such that the slotguides the motion of the piston rod.

With reference to FIG. 5, the latch actuator may be biased to extend thecylinder as shown in this figure to latch the dampening cylinder 200 tothe housing 300. In operation of this embodiment, when the latch 330 isshown in the position of FIG. 5, the latch gripping teeth 344 engage theteeth 368 carried by the cylinder housing 202 and prevents changes inelevation of the cylinder housing 202 in relation to vibration dampenerhousing 300 and thus relative to the seat support 20. When in thisposition, the latch arm 334 has been pivoted in the direction of arrow410 (clockwise in this figure) to engage the latch and latch grippingsurfaces. When latched as shown in FIG. 5, the vibration dampener isoperable to dampen vibrations of the seat. Conversely, in the event theelevation of the seat is to be changed in this embodiment by operationof the air spring 170, the latch 330 is unlatched. More specifically,fluid pressure is delivered to port 394 of actuator 390 causing theretraction of piston rod 392. This motion, guided by the slot 406, iscoupled via the link 400 to the flange 338 and results in pivoting ofthe latch 330 in the direction of arrow 412 as shown in FIG. 6. As aresult, the latch surface 344 is disengaged from the latch grippingsurface 368. When in the disengaged state, the cylinder housing 202raises or lowers as the seat height adjustment takes place.Consequently, dampening forces are not applied during seat heightadjustment. Moreover, following seat height adjustment and re-engagementof the latch to the cylinder, in this example the same dampening forceis applied to the seat as was applied immediately before the seat heightadjustment took place. Although less advantageous, it is also possibleto retain dampener cylinder 202 in a latched state during all orportions of the seat height adjustment (in which case the dampener wouldtypically be operable over a broader range of motion). In this lattercase, the dampener may be unlatched for shifting to the desired newposition following all or portions of the seat height adjustment.However, by unlatching the dampener over the full seat heightadjustment, the damper design can be optimized to dampen motion solelyover a more limited range of motion rather than over the entire range ofthe seat height adjustment. As another alternative, although lesspreferred, the dampener cylinder 201 and/or the housing 300 may becarried by a mechanism which permits the entire assembly to move ratherthan coupling and decoupling the dampener cylinder. For example, thehousing may be supported by a fluid actuated screw jack which adjuststhe position of the housing and thereby the dampener to accommodate seatheight adjustments.

An alternative form of vibration dampening module 430 is shown in FIG.9. Vibration dampener 430 includes a shock absorber or vibrationdampener 432, which may be like dampener 201 of FIG. 4, having anexterior housing 434 and a rod 436. A piston (not shown) coupled to rod436 dampens vibrations of the seat as the rod 436 moves. Vibrationdampener 430 also includes an exterior housing, in this case formed oftwo generally U-shaped housing sections 442, 444. The housing section442 includes side flanges 446, 448 and a rear flange 450. The housingsection 444 includes side flanges 452 and 454, and a base or back flange456 which interconnects the flanges 452, 454. When the housing isassembled, the housing section 444 nests within housing section 442 withthe sets of leg flanges 446, 452 and 448, 454 abutting one another. Whenassembled, pivot receiving apertures 460, 462 through the respectiveflanges 446, 452 are aligned. In addition, pivot receiving openings 464,466 of the respective flanges 448 and 454 are also aligned. A pivot axis468 extends through these aligned openings. The housing is pivoted tothe base 30 (FIG. 1) in the same manner as housing 300 with pivot axis468 corresponding to apart the pivot axis 306 of the FIG. 4 embodiment.End flange 456 has a pair of spaced-apart openings 470, 472 which arealigned with a corresponding pair of openings (not shown) in the backwall 450 of housing section 442.

In the FIG. 9 embodiment, the latch 480 includes first and secondelongated pivot arms 482, 484. Arm 482 includes a pivot pin portion 486which is inserted through opening 470 when the module is assembled. Anopposed pivot pin portion projects in the opposite direction through thecorresponding opening in the back wall 450. In the same manner, arm 484includes a pivot pin portion 488 which is pivotally received within theopening 472 when the module is assembled. A pivot pin portion opposed toportion 488 extends in the opposite direction from the opposite side ofarm 484 into a pivot pin receiving opening through back wall 450. Thearms 482, 484 are thus capable of rocking back and forth about therespective axes through pin portions 486, 488.

The upper end portions 500, 502 of the respective arms 482, 484 are eachprovided with a respective latching surface 504, 506. In the illustratedembodiment, the latching surfaces 504, 506 each face toward the cylinder434. A friction enhanced latching surface, which may be roughened or maycomprise a plurality of transversely extending teeth on the respectivesurfaces 504, 506, are provided for gripping the cylinder 434 when thecylinder is latched. The outer surface of the cylinder 434 includes orsupports a friction enhanced latch gripping surface which may comprise aroughened surface. In the illustrated embodiment, the latch grippingsurface comprises elongated rows of teeth extending in a directionparallel to the longitudinal axis of the cylinder as indicated at 512,514 in FIG. 9, are welded or otherwise secured to the exterior of thecylinder 434. When arm 482 is pivoted counter clockwise as indicated byarrow 516 in FIG. 9 and arm 484 is pivoted clockwise as indicated byarrow 518 in this figure, the latching surfaces 504, 506 of the arms482, 484 engage the teeth 512, 514 carried by the cylinder housing. Whenlatched, the dampener 432 operates in the same manner as the dampener200 of FIG. 4 when it is in an engaged or latched condition. Conversely,when arms 482 and 484 are pivoted in respective directions opposite toarrows 516, 518, surfaces 504, 506 become disengaged from the teeth 512,514. As a result, the dampener 432 is free to move with the seat as theseat height is adjusted by the air spring 170 or other seat heightadjuster.

An actuator such as a pneumatic cylinder 520 is provided for selectivelypivoting the arms 482, 484 during operation of the vibration dampeningmodule 430. Actuator 520 includes a piston rod 522 coupled to a U-shapedclevis 524. A first link 526 is pivotally coupled at one end portion toclevis 524 for pivoting about a pivot axis 528. The link 526 is alsopivoted at its opposite end portion to a lower end portion 530 of arm482 such that link 526 may pivot about a pivot axis 532. Similarly, alink 534 is pivoted at one end portion to the clevis 524 for pivotingabout the axis 528. In addition, the opposite end portion of the link534 is pivoted to a lower end portion 536 of arm 484 for pivoting aboutan axis 538. When piston rod 532 is fully extended (and the rod may bebiased in this position), the arms 482, 484 assume the positionindicated in FIG. 9 to latch the dampener 432 to the housing sections442, 444 and thereby to the base 30 (FIG. 1) of the seat support 20. Incontrast, the delivery of pressurized fluid to a port 540 of actuator520 causes rod 522 to retract. In response, the links 526, 534 draw thelower end portions 530, 536 of arms 482, 484 inwardly. When thishappens, the arms 482, 484 pivot in a direction opposite to arrows 516,518 to release the surfaces 504, 512 and 506, 514 from one another sothat the dampener 432 is free to move during seat height adjustment. Theactuator 520 may be operated in the same manner as actuator 390 toaccordingly control the latching and unlatching of vibration damper 430.One suitable form of actuator 390, 520 is a spring biased pneumaticcylinder Model BLC 2T2 from Sprague Controls of Canby, Oreg. Also, thebracket 234 for receiving a link, like link 232 in FIG. 1, may bemounted to cylinder housing 434 for reasons explained above inconnection with FIG. 1.

The dampening shock absorbers 201 and 432 of FIGS. 4 and 9 may beconventional shock absorbers of the type which apply a linear dampeningforce in opposition to seat vibrations. Also, any suitable mechanism fordampening vibrations may be used in place of the piston containingdampening cylinders 201, 432. However, the illustrated shock absorbersmay be of the type which applies a non-linear dampening force to seatvibration.

An exemplary dampener of this type is illustrated in FIG. 10 andexamples of its operation is indicated in FIGS. 10A and 10B. Non-lineardampeners are not known to have been heretofore used to dampen seatvibrations. However, non-linear dampening cylinders are available fromcompanies such as Monroe Auto Equipment Company.

The specific shock absorber embodiment of FIG. 10 (with the components360, 370 in FIG. 8 eliminated for convenience), includes interior andexterior chambers 600, 602. Chamber 600 includes fluid charged regions604, 606 above a fluid charged area 606. Makeup fluid is stored inchamber 602 (e.g. below the dashed line 607 in this figure), with theflow of makeup fluid between the two chambers controlled by conventionalvalve 608. Chamber 602 includes a gas charge (e.g. above the dashed line607 in this figure). A piston 610 is mounted to the piston rod 206 forsliding within the chamber 600. A biasing spring 612, positioned betweenpiston 610 and an interior stop 614, urges the piston toward a homeposition indicated at 616 in FIG. 10. The spring 612, which may have aspring rate of about fifty Newtons per mm (although this is variable)may be a conical spring which collapses upon itself as it is compressedto reduce the amount of space required by the spring when fullycompressed to thereby reduce the overall required operating length ofthe dampener 201. The interior wall bounding chamber 600 may be providedwith one or more longitudinally extending grooves (two being indicatedat 620, 621). The grooves control the rate at which fluid bypasses thepiston 610 as the rod 206 is extended and retracted to thereby controlthe applied dampening force. The cross-sectional area of the grooves maybe greater at home position 616 than at areas further removed from thehome position to vary the dampening force with the distance the pistontravels from the home position. For example, the grooves may be taperedto reduce their cross-section, moving further away from the homeposition. Alternatively, more grooves may be provided closer to the homeposition than further away to decrease the resistance to lessermovements of the piston and rod away from the home position. Stepwisevariations in the applied dampening force may also be provided, forexample by including stepped differences in the cross-sectional area ofthe grooves at specific locations along the length of the cylinder.Also, the dampening force may be varied non-linearly with distances fromthe home position. For example, for greater movements of the piston fromthe home position, corresponding to greater vibrations of the seat, thedampening force may be increased non-linearly to a much higher levelthan applied to minor deviations or movements from the home position.Also, the dampening force may be constant for certain predetermineddeviations from the home position and then increase as thesepredetermined deviations are achieved. For example, the bypass groovesmay be of a constant cross-sectional dimension over these predetermineddeviations and then decrease in cross-sectional dimension after thepredetermined deviations from the home position are exceeded. As thepiston approaches the design limits of its maximum compression and/orextension, bumpers 626 and 628 may be engaged and compressed to cushionthe latter movements of the shock absorbing damper.

In addition, in the illustrated construction, differing forces may beprovided in opposition to downward movements of the seat than inopposition to upward movements of the seat. In addition, greater travelof the dampening cylinder may be allowed in response to vibrations inone direction than another. More specifically, in an illustratedapproach, lower dampening resistance is provided to counteractreductions in seat height (compression of cylinder 202) than tocounteract increases in seat height (extension of cylinder 202). Also,further travel is allowed by the dampening cylinder 202 in response tocompression (seat height reduction) than in extension. Typically,greater energy needs to be absorbed in compression (for example, if atruck hits a bump, the deck or floor of the truck tends to move upwardlytoward the seat) than in extension. By providing a lesser dampeningforce in response to compression and permitting greater dampeningmovement of the cylinder in response to compression, a smoother ride isprovided.

The profile of the dampening force applied in response to travel of thepiston 610 may be varied. However, in one specific example, thedampening piston 610 is permitted to travel forty millimeters incompression (including bumper compression at the end of the dampenerstroke) and twenty-five millimeters in extension (including bumpercompression).

FIG. 10A (not to scale) illustrates the dampening applied in response totwo velocities of vibration induced seat travel. Specifically, at arelatively low velocity of 4.7 inches per second, an exemplary dampeningforce profile in compression and extension is shown in dashed lines inFIG. 10A. In addition, an exemplary dampening force profile atrelatively high velocity of 26.7 inches per second is shown in the solidlines in FIG. 10A. As can be seen in this figure, in this example, froma distance of about 15 mm in compression from the home position to adistance of about 10 mm in extension from the home position, the crosssection at each of the grooves remains constant. Consequently, over thisrange the applied dampening force is constant. This dampening forceresists the bulk of the vibrations, as most vibrations cause arelatively small range of seat motion. From about 10 mm of extension toabout 12 mm of extension, in this example the cross-sectional dimensionof the grooves is reduced (in this case, the grooves are tapered suchthat the resistance force increases generally linearly over this range).Again, stepwise or other variations can be provided. In this example,the resistance force varied non-linearly from the home position. If thevariation were linear, the slope of the dampening force versus distanceof travel from the home position would be constant. At about 12 mm ofextension, the cylinder wall grooves have ended. The resistance againstextension continues to increase, but at a different rate. When thebumper is engaged, the resistance increases more sharply and, in theory,goes to infinity after the bumper is fully compressed at the desiredmaximum extension, in this case, twenty-five millimeters. Conversely,looking at the compression side of the profile, from about 15 mm ofcompression to about 17 mm of compression, the cross-sectional dimensionof the grooves is reduced so that the resistance against compressionincreases. Thus, the resistance against compression has also variednon-linearly from the home position. From about 17 mm of compressionthrough the engagement of the bumper contact, the grooves in thisspecific example have ended. Resistance against compression continues toincrease and increases more sharply approaching bumper engagement.Following full compression of the bumper, the resistance againstcompression, in theory, goes toward infinity. In this specific example,forty millimeters of maximum compression is permitted. As can be seen inFIG. 10A, in general, there is a hysteresis effect to the profile asindicated by the arrows shown in this graph.

Although variable, in a specific example, at point 650, the end of thegrooves with the piston extending at high velocity, a seven hundredpound dampening force is applied. In contrast, in this example, at highvelocity and at the end of the grooves with the piston moving incompression, at point 652 the dampening force is sixty hundred fiftypounds. Also, at the low velocity of 4.7 inches per second, at point654, which corresponds to the end of the grooves when the piston isextending, a two hundred pound dampening force is applied. Conversely,at point 656, corresponding to the end of the grooves with the pistonmoving at this low velocity in compression, a dampening force of onehundred points is applied.

FIG. 10B illustrates an exemplary response of the dampening cylinder 10as it is extended and compressed at two sinusoidally speeds S 1 and S 2. The speeds S 1 and S 2 are at a maximum at about the center of therange of motion with speed S 1 being greater than S 2 . Betweenlocations 659 and 661 the bypass grooves are of a constantcross-sectional dimension and the applied resistance force is constantfor a given speed S 1 , S 2 and in a given direction (extension orcompression). As can be seen in this example, in general at a givendisplacement from the home position 663, the magnitude of the resistanceagainst compression (below the X axis) is lower than the magnitude ofthe resistance against extension (above the X axis). At location 661,and over a distance in this case of about 2 mm (from 10 mm extension to12 mm extension) the cross-sectional dimension of the bypass groovestaper. At location 667 engagement of the bumper commences. The maximumextension is indicated at 669. In the other direction from the homeposition, from 15 mm to 17 mm, in this example, the bypass grooves taper(location 659 to location 671). At location 673, the cushioning bumperis engaged with maximum compression occurring at location 675. Thedashed line 677 indicates the expected force/displacement curves atspeed S 2 if no bypass grooves are provided.

FIGS. 11-13 illustrate an alternative form of seat suspension systemwith a latch external to a dampener and which is operable independentlyof the dampener. For convenience, components in FIG. 11 which correspondto similar components in FIGS. 1-3 have been identified with the samenumbers with the superscript (′). Consequently, these correspondingcomponents will not be discussed in detail, although they do illustratesome of the wide variations of configurations which may be used forthese components.

The illustrated latch 220′ includes a sector plate 700 pivotally mountedto the base 30′ for pivoting about the axis 34′. The sector plateincludes an arcuate slot 702. A pin 704 extends from link member 24′through the slot 704. The sector plate is thus free to pivot relative tolink member 24′ and about axis 34′ within the limits defined by the slot702. Sector plate 700 includes an arcuate outer edge portion 706 whichcomprises a latch engaging surface. The latch engaging surface may befriction enhanced and may include a plurality of teeth, some beingindicated at 708 in these figures.

An upwardly extending bracket 720 having parallel spaced-apart legs 722,724 may be included in the latch construction. The legs 722, 724 aremounted for pivoting about the axis 34′. An upper portion 726 of bracket720 may be of an inverted, U-shaped construction, with side flanges 728and 730 interconnected by a base or top portion 732. The upper end ofrod 206′ of the shock absorber 201 is pivoted to side flange 728 of thebracket 720 so as to be pivotal about an axis 734. The leveling valve230′ is supported by side flange 730. A latch arm 740 is pivoted at 742to the bracket side flange 728. In addition, a latch arm extension 744extends from an upper end portion of latch 740 and has an uppermostportion 746 which is pivoted for movement about the axis 734. A lowerportion of latch arm 740 is pivotally coupled to a link 752 for pivotingabout an axis 754. Link 752 supports a latch actuator, such as apneumatic actuator 760. In this case, the pneumatic actuator 760 ispivoted to link 752 for pivoting about an axis 762. The illustratedactuator 760 may be the same as actuator 390 (FIG. 1) and, in this case,includes a piston coupled to a rod 764. The rod 764 has its upper endportion 766 pivoted to side flange 722 for pivoting about a pivot axis768. The latch arm 740 includes a latch surface for engaging the latchgripping surface of the sector plate 700. One form of latch grippingsurface is indicated at 770 and comprises a plurality of teeth sized andpositioned to engage the teeth 708 of the sector plate when the latch isin a latched condition, as shown in FIGS. 11 and 12.

To unlatch the latch, actuator 760 is activated to, in this case, extendthe rod 764, as shown in FIG. 13. With the above-described linkagearrangement, when rod 764 extends, for example in respond to delivery ofpressurized fluid to port 772 of the actuator 760, the latch arm 740pivots in the direction of arrow 782 in FIG. 1310 (clockwise in thisfigure). This shifts the lower end portion 750 and the gripping surface770 of latch arm 740 away from the teeth 708 of the sector plate 700.When unlatched as shown in FIG. 13, links 24′ and 26′ may be moved bythe air spring 270′ to adjust the seat elevation without changing theposition of the shock absorbing damper 201′. That is, link 24′ may bemoved relative to the sector plate 700. After the seat has been adjustedto the desired elevation, piston rod 764 may be retracted to pivot arm740 in a direction opposite to arrow 782 and into engagement with theteeth on the sector plate as shown on FIG. 12.

The latch 220′ may be controlled in the same manner as the latch 220 ofFIGS. 1-3. For example, the latch may be shifted to its unlatchedposition during the entire time the set height is being adjusted by airspring 270′ and then latched following seat height adjustment so thatthe same dampening force is applied immediately after seat heightadjustment as was applied immediately before seat height adjustment.Alternative latch control approaches may also be used, as previouslydescribed.

In the construction of FIGS. 11-13, the leveling valve 230′ may operatein the same manner as leveling valve 230. That is, with the latch in alatched condition and in the event the load on the seat is varied (forexample, the occupant of the seat gets off the seat), the seat will tendto raise. When the seat raises beyond the upper limit established byleveling valve 230, the leveling valve controls the exhaustion of gasfrom the air spring 270′ to readjust the position of the seat. In theillustrated construction, the seat position is readjusted toward itsoriginal home position. Conversely, when a load is reapplied to the seatand the seat lowers in elevation beyond a lower limit established byleveling valve 230′, the leveling valve 230′ operates to cause thedelivery of additional air to air spring 270′ to again raise the seattoward the home position. When the latch is unlatched, the seatelevation may be freely adjusted as the leveling valve 230′ is decoupledand thus inoperative when the latch is unlatched during intentional seatheight adjustment by the air spring 270′.

FIG. 14 illustrates an alternative form of shock absorber 800 which maybe utilized in the disclosed embodiments of the seat suspension system.The illustrated FIG. 14 shock absorber includes a lower shock absorbingsection 802 within which an internal piston may be provided and coupledto a piston rod 804. A housing 806 defines a biasing spring receivingchamber 808 within which first and second biasing springs 810, 812 areprovided. An internal spring separation plate 814 is mounted to the rod804. With this construction, spring 810 resists compression of thedampener and corresponding movement of the rod 804. In contrast, thespring 812 resists extension of the rod 804. The biasing forces exertedby the springs may be different and the distance of travel incompression and extension may be varied. As one specific example, spring812 may provide twenty pounds force per inch resistance with a maximumextension of twenty-five millimeters, while spring 810 may provide fortypounds force per inch compression with a maximum compression distance offorty millimeters, the distances being from a home position indicated at816 in FIG. 14. At the home position in the illustrated form of shockabsorber, the springs exert fifteen pounds force against one another.

Again, other vibration dampeners, including other forms of shockabsorbers, may be utilized in the illustrated seat suspension systems.

FIGS. 15, 16, 16A and 17 illustrate another form of latch mechanismwhich may be used in the illustrated seat suspension embodiments. Again,for purposes of convenience, components of the seat suspension of FIG.15 and the related figures which correspond to components of FIG. 1 areillustrated with the same number as utilized in FIGS. 1-3, except with adouble prime superscript (″). These corresponding components will not bedescribed in any detail.

The vibration dampener 220″ comprises a rod gripping latching assembly870 coupled at its upper end portion 872 to the seat support member 22″at a location rearwardly of pivot 32″. The lower end portion of thevibration dampener 220″ is pivoted to base 30″ at a location forwardlyof pivot 38″. More specifically, the illustrated rod gripping latchassembly 870 is pivoted to downwardly projecting ears, one being shownat 874 in FIG. 15, at the underside of seat supporting member 22″ forpivoting about a pivot axis 876. The piston rod 206″ in this embodimentis of an extended length and passes through the rod gripping latchassembly 870. When in a latched condition, the rod is gripped by thelatch assembly 870 so that it does not move relative to seat supportmember 22″. Consequently, the dampener 200″ is operable to dampen seatvibrations. When unlatched, the rod 206″ is free to slide relative tothe rod gripping latch assembly 870. Thus, for example, the rod may bereleased during seat height adjustment by air spring 270″ so that theelevation of the seat may be adjusted to a new desired elevation. Thelatch may then be operated to re-engage the rod 206″ and again apply thedampening force to the seat support and the seat. Consequently, thedampening force applied to the seat may be the same immediately beforeand after a seat elevation adjustment by air spring 270″. The latchingmechanism 220″ may be controlled in various manners, such as previouslydescribed in connection with the latching mechanism 220.

An optional positioning sensor, such as leveling valve 230″, may beincluded in this system, as well. Leveling valve 230″ is coupled bylinks, including link 232″, to a collar 878 which is secured to rod 206″for movement with the rod. Leveling valve 230″ may be operated in thesame manner as leveling valve 230 and, hence, its operation will not bedescribed in detail.

It should be noted that the construction of FIG. 15 is less compact thanthe construction of FIG. 1 due to the elongated nature of piston rod206″. To reduce the overall length of the construction, latch mechanism870 may be positioned adjacent to shock absorber 200″ on a separate rodor other element which is to be gripped. In this latter case, the shockabsorber 201″ may be coupled to this alternative rod or element which isto be gripped.

With reference to FIGS. 16, 16A and 17, the illustrated FIG. 15 form ofrod gripping latch assembly will next be described. More specifically,the illustrated latching assembly 870 includes an outer cylindricalhousing 890 defining an upper chamber 892 and an enlarged lower chamber894. Upper and lower end caps 896, 898 are threaded or otherwise securedto housing 890 to enclose the respective ends of the latch mechanism870. A piston 900 is positioned within housing 890 and has an upperportion 902 and a lower enlarged portion 904. Upper portion 902 supportsan O-ring seal 906 which engages the interior wall of housing 890 in theregion of upper chamber 892. Lower enlarged portion 904 of piston 900carries an O-ring 908 which sealingly engages the interior wall ofhousing 890 in the region of the lower chamber 894. A biasing spring 910is positioned between end cap 898 and piston 900.

The assembly also includes at least one rod gripping element and, in theillustrated form, includes four such elements 912, 913, 914 and 915.Each of the illustrated elements 912 through 915 is spring biased awayfrom the rod 206″. For example, the rod gripping elements may besupported by a spring 916 having an enlarged upper end portion 918secured between the cap 896 and housing 890. The lower exterior surfaceof the rod gripping elements, such as indicated at 918 for element 912,may taper downwardly into a wedge-shaped configuration. With piston 900in the position shown in FIG. 16, an upper surface of piston 902 bearsagainst the wedge surfaces 918 to urge the rod gripping elements 912-915against the rod. The rod 206″ may include a friction enhanced outersurface to facilitate gripping of the rod by the rod gripping elements.In addition, the surface of gripping elements 912, 915 which engages therod may also be friction enhanced. As a specific example, a plurality ofconcentric ridges, such as indicated at 920, may be provided along thelength of rod 206″. These ridges, although not apparent from thefigures, may extend along a region of rod 206″ of a length correspondingto the full range of seat height adjustment so that, regardless of theheight to which the seat has been adjusted, ridges 920 are in positionfor gripping by the elements 912-915 at all seat height adjustments.Corresponding grooves may be provided as indicated at 922 in the rodgripping surface of the elements 912-915. In effect, teeth are thusprovided on the surfaces 920 and 922 which mesh together to lock the rod206″ to the latching assembly 870 when piston 900 is positioned as shownin FIG. 16.

With reference to FIG. 17, to disengage the latch assembly 870 from therod 206″, pressurized fluid such as air is delivered via line 924 tothat portion of chamber 894 between the seals 906 and 908. This shiftspiston 900 downwardly as shown in FIG. 17. Due to the spring bias on rodengaging elements 912-915, these elements shift outwardly away from therod (see arrows 925) so as to disengage the surfaces 920, 922 from oneanother. This permits sliding movement of the latch assembly 870 ineither direction along the rod as indicated by double headed arrow 926during seat height adjustment. Following seat height adjustment,pressure may be relieved on line 924, permitting spring 910 to shiftpiston 900 upwardly to cause elements 912-915 to re-engage the rod 206″.

Thus, the latching mechanism 870 also allows the use of a dampenercapable of applying a non-linear dampening force to the seat. Duringseat height adjustment in this example, however, the home position ofthe dampener remains at the same elevation. That is, in this case, theseat can be moved relative to the dampener rather than moving thedampener with the motion of the seat. Again, latching mechanism 870 maybe controlled in the same manner as previously described for latchingassembly 220.

FIG. 17A illustrates another form of latch mechanism which is similar tothat shown in FIGS. 15, 16, 16A and 17 and which may be used in theillustrated seat suspension embodiments. For purposes of convenience,components of the seat suspension latch of FIG. 17A which correspond tocomponents of the embodiment of FIGS. 15, 16, 16A and 17 are illustratedwith the same numbers. These corresponding components will not bedescribed in any detail. The latch shown in FIG. 17A is longitudinallymore compact than the latch shown in FIGS. 16 and 17 and thus may beincluded, for example, in applications where space limitations aregreater.

With reference to FIG. 17A, although a cap such as 898 in FIG. 16 may beused, a mechanically simple spring retainer 899 is shown for retainingthe biasing spring 910 in position. An annular notch 901 is providedaround the interior perimeter of housing 890 and adjacent to the lowerend of this housing. The spring retainer includes fingers 905 which fitwithin notch 901 when the spring retainer 899 is installed. Thesefingers are deflected during installation of the retainer 899 and thensnap into the notch 901 when in position. An annular shelf 907 isprovided near the lower end of housing 890 and above the notch 901. Ahorizontal radially extending disk-like body portion 911 is included inthe illustrated retainer 899. The upper surface of the distal end of thebody portion 911 engages the shelf 907. Fingers 905 project from thebody portion. A central portion 913 of body portion 911 is raised asshown to define a seat which is inserted into the interior of the spring910. A downwardly extending collar portion 915 of body 911 surrounds theshaft 206″. The retainer 899 may be stamped or otherwise formed from asingle piece of sheet metal or other suitable material.

The locking elements 912, 914 (again, one or more such locking elementsmay be provided, with four such elements being included in theillustrated embodiment), each include a friction enhanced surface, inthis illustrated case a toothed shaft gripping surface 922. The surface922 selectively engages a friction enhanced surface on shaft 206″, inthis case toothed surface 920, when the shaft is engaged by the latch.

The gripping elements 912, 914 are shaped and biased toward an unlatchedstate or condition in which surfaces 922 and 920 are disengaged from oneanother. When spring 910 urges piston 900 upwardly as shown in FIG. 17A,surfaces 918, 919 engage one another. As a result, the surfaces 922 and920 are shifted into cooperative latching engagement. Conversely, asexplained previously in connection with FIGS. 16 and 17, whenpressurized air is delivered via air supply line 924 to chamber 894, thepiston 900 shifts downwardly from the position shown in FIG. 17A. As aresult, the surfaces 920, 922 disengage one another. When disengaged,because of the biasing on latching elements 912, 914 (and elements 913and 915, not shown in FIG. 17A), the latch gripping elements arereleased from the shaft.

In the specific example shown, this biasing of elements 912, 914 isaccomplished by an annular wave spring 925 which engages an undersurfaceof a radially outwardly projecting flange 923 of each of these latchgripping elements. A gap 927 is provided between the upper surface offlange 923 and the under surface of cap element 872. Consequently, whenpiston 900 moves downwardly in FIG. 17A, wave spring 925 pivots thelatch elements 912, 914 about a rocking or pivot point 917 with flange923 moving toward the cap 872. This in turn shifts the latch surfaces922 away from the rod 206″, releasing the rod from the latch grippingelements. An inwardly projecting rib portion 921 of the latch elements912, 914 is positioned within a radially inwardly extending annularnotch 929 formed in cap piece 872. Consequently, the latch elements 912,914 do not shift longitudinally within the housing 890 when piston 900is moved.

Again, the construction of FIG. 17A illustrates one variation of thelatch of FIGS. 16 and 17 which is longitudinally more compact. Also, thelatch of FIG. 17A may be used in the orientation shown in FIG. 17A or inany other orientation, such as in the opposite (e.g. rotated 180degrees) position from the position shown in this figure.

FIG. 18 illustrates yet another embodiment of a seat suspension systemhaving features in common with the previously described systems.Elements in common with those previously described have been given thesame numbers, with a triple prime (′″) superscript and for this reasonwill not be described in detail. In the embodiment of FIG. 18, the seatsupport member 22′″ is raised and lowered by air spring 270′″ byrespectively inflating and deflating the air spring. Vertical motion ofthe seat member 22′″ is guided by a rod 930 extending upwardly from thefloor 14′″ of the vehicle. A slide 932 is slidably mounted to the rod930. A latch 934 selectively couples the slide 932 to the rod. Duringseat height adjustment, the latch 934 may be operated in the same manneras previously described for latch mechanism 220. Thus, for example, thelatch 234 may be unlatched to permit sliding of slide 232 upwardly anddownwardly along rod 930 as the air spring 270′″ raises or lowers theseat. In addition, as an example of this operation, after the seatheight has been adjusted, the latch 934 may be actuated to latch theslide 932 to the rod. A biasing spring 936 urges the slide 932 to acentral or home position. Enlarged collars 938, 940 are provided at therespective upper and lower ends of the slide 932. Collar 938 engages thebottom surface 942 of seat support member 22′″ to limit the upwardmotion of the seat in response to vibrations. Conversely, downwardmotion is limited by the extent to which collar 940 may travel in adownward direction before spring 936 is fully compressed. The slide 932has a central portion which passes through an opening 948 through seatsupport member 22′″. The opening 948 is sized to prevent passage of thecollars and spring 936 through the seat support member. A damper 200′″,which may be a simply shock absorber, engages the upper surface 946 ofseat support member 22′″ and is coupled by links 950, 952, 954 and 956to the slide 936 and the seat support member 22′″. When the seatvibrates, link 952 pivots about pivot a 958, with this motion beingdampened by shock absorber damper 200′″. Link 954 supports pivot 952 topermit this motion.

A seat position sensor, such as leveling valve 230′″, may be used toadjust the inflation of the air spring and the seat elevation uponchanges in loading on the seat when the slide is latched to the rod 930.Leveling valve 230′″ is coupled by a link 232′″ to the collar 938 forthis purpose.

FIGS. 19-22 disclose one form of a suitable pneumatic circuit and valvefor the illustrated seat suspension embodiments. It should be understoodthat the valve arrangement and pneumatic circuits may be varied.However, the circuitry described below utilizes a valve (or two separatevalves) actuated by a single lever or single switch for simultaneouslycontrolling both seat elevation adjustment and the latching andunlatching of a latch mechanism. Although this construction isadvantageous, separately actuated valves may also be used foraccomplishing these results.

FIG. 19 illustrates the seat 12 shown schematically on a seat support20. The seat may be raised and lowered as previously described, such asby the air spring 270. In addition, the system may include a latch, suchas latch 220. Air spring 270 and latch 220 are shown schematically inFIG. 19. In addition, the optional automatic leveling valve 230 is alsoshown in this figure coupled to the air spring 270. In addition, a valve960 is shown for controlling both the air spring 270 during seat heightadjustment and the latch 220.

With reference to FIG. 20, pressurized air is supplied along a line P toboth the valve 960 and the leveling valve 230. Exhaust lines E are alsoshown coupled to these valves. In the configuration shown in FIG. 20, noautomatic leveling is occurring, the latch actuator 390 is in positionto latch the latch mechanism 220, and the seat height is not beingadjusted. Thus, the air spring line AB is neither being supplied withpressurized air nor being exhausted through either of the valves 960 or230. In this situation, assume the seat height changes while latch 220is latched. In such a case, the link 232 shifts valve 230 eitherupwardly or downwardly. If the seat has raised sufficiently to operatethe valve 230, the valve 230 shifts upwardly in FIG. 20, coupling airspring line AB through valve 230 to exhaust line E, resulting indeflation of the air bag until such time in this example as the seat hasbeen lowered to the point where the auto leveling valve no longeroperates. Conversely, in this situation, if a load is added to the seat,causing the seat to depress or lower, link 232 causes valve 230 to shiftdownwardly in FIG. 20. If the seat lowers sufficiently to operate thevalve 230, pressure supply line P is coupled through valve 230 to theair spring line AB so as to inflate the air spring. The air spring willcontinue to inflate in this example until auto leveling valve 230 is nolonger actuated. As previously described, for example in connection withFIG. 1, if the dampening valve is unlatched and the seat height isadjusted, link 232 does not operate the auto leveling valve 230.

Next, assume the seat occupant desires to raise the elevation of theseat. In this case, a manual actuation lever 962 is shifted upwardly inFIG. 20. This couples the pressure supply line P through valve 960 tothe air spring line AB, causing the air spring to inflate and raise theseat. The valve 960 may be biased to the neutral position shown in FIG.20 so that, upon releasing of the lever 962, the valve returns to theposition shown in FIG. 20 and further inflation of the air spring stops.In addition, in the circuit illustrated in FIG. 20, as the valve 960shifts upwardly in this figure, the line P is also coupled through thevalve to the latch actuator line AC. Consequently, pressurized fluid isdelivered to the latch actuator 390, causing the latch actuator torelease the latch. This relieves the dampening force from being appliedto the seat. After the seat reaches its desired elevation and valve 960returns to the position shown in FIG. 20, line AC is again exhausted,causing latch actuator 390 to control the latch 220 to latch thedampener mechanism into its operative dampening force applying state.

If it is desired to lower the seat, lever 962 is moved downwardly. Inthis case, line AB is coupled through valve 960 to the exhaust line E,causing the deflation of the air bag. Simultaneously, pressurized air isdelivered from line P to line AC, causing the latch actuator 390 torelease the latch 220 as described above for the case when the seat wasbeing raised.

FIGS. 21A-21C illustrate one form of valve 960 having a common housing966 within which a slide plate 964 is positioned for accomplishing thedual functions of controlling the latch and seat height adjustment asdescribed above in connection with FIG. 20. In contrast, in FIG. 20valve 960 had two valves, one for the seat height adjustment control andone for latch/unlatch control, which were controlled by a commonactuator (e.g. lever 962). As yet another alternative, each of these twovalves may have separate actuators which may be mechanically orelectronically linked for simultaneous operation. FIG. 21A correspondsto the condition of valve 960 depicted in FIG. 20, with the latchactuator 390 latched (line AC being exhausted) and the seat in aconstant position (line AB being neither supplied with pressurized airor being exhausted through the valve 960).

FIG. 21B illustrates the slide plate 964 shifted to a position wherebyvalve 960 controls the lowering of the seat and the unlatching of thelatch 220. That is, air spring supply line AB is shown exhausted,resulting in a deflation of the air bag. Simultaneously, the pressureline is coupled to line AC to cause the latch actuator to unlatch thelatch.

In FIG. 21C, the valve slide plate 964 is shown in a position forraising the seat. In this case, pressure line P is coupled to line AB toinflate the air spring. Simultaneously, pressure line P is coupled toline AC to cause the latch actuator to unlatch the latch 220. In FIGS.21A, 21B and 21C, the slide plate 964 is shown in a common housing 966.As previously described, additional control approaches may also be usedin operating the latching mechanism 220 and seat height adjuster. Thus,although the above approach is advantageous, other approaches may beused by which these devices operate in other sequences (for example, thelatch actuator being operated during only a portion of a time the seatheight adjuster is operated, or in a sequential manner).

FIGS. 22A-22E illustrate a specific form of dual function valve 960.Valve 960 includes a cover 970 overlaying housing 966. The cover has aslot 972 through which the lever 962 projects. The lever 362 may beraised and lowered as indicated by the arrows in FIG. 22A from thecentered position shown in this figure. FIG. 22B illustrates theconnection of lever 962 to the slide plate 964 and shows the lever andslide plate comprised of a one-piece homogeneous unitary construction.These elements may, for example, be injected molded of plastic. A wavespring 974 biases the slide plate against O-ring seals surrounding portsthrough housing 966. These ports are connected to the respective linesP, AB, AC and E. One of these O-rings is indicated at 975 in FIGS. 22Aand 22B. A coil spring 976 is coupled to lever 962 and engages flangesprojecting inwardly from cover 970 (one such flange being indicated at978 in FIG. 22B). Spring 976 biases the lever 962 to its centeredposition. Suitable flow paths are defined in slide plate 964 andcorrespond to the centered position (FIGS. 21A and 22C); the lower seatposition (corresponding to FIGS. 21B and 22D); and the raised seatposition (corresponding to FIGS. 21C and 22E). Again, other valvearrangements and controls may be used, for example, electronic controls.However, the specifically illustrated approach employs a single switchlever 962 for simultaneously controlling the raising or lowering of theseat by the seat height adjuster and also latching and relatching of alatch mechanism utilized in a number of the disclosed embodiments.

Having illustrated and described the principles of our invention withreference to several embodiments, it should be apparent to those ofordinary skill in the art that these embodiments may be modified inarrangement and detail without departing from these principles. We claimall such modifications as fall within the scope of the following claims.

What is claimed is:
 1. A vibration damper for a seat suspension systemof the type which supports a seat above the floor of a vehicle, the seatbeing raisable and lowerable to support the seat at various selectedelevations relative to the floor of the vehicle, and wherein movement ofthe seat from a selected elevation in response to vibrations ispermitted, the vibration damper comprising: a first member adapted forcoupling to one of the vehicle and seat; a shock absorber adapted to becoupled to the other of the vehicle and seat; and a latch adapted toselectively couple the first member to the shock absorber such that whenthe shock absorber and first member are coupled together the shockabsorber applies a dampening force to the scat at least partially inopposition to elevation changes of the seat from a selected elevation inresponse to vibrations, and such that when the shock absorber and firstmember are decoupled from one another the shock absorber is relievedfrom applying the dampening force to the seat.
 2. A vibration damperaccording to claim 1 in which the first member comprises a housinghaving an interior and an exterior, the shock absorber beingsubstantially positioned within the interior of the housing, and whereinthe latch is carried by the housing and selectively couples anddecouples the shock absorber to and from the housing to therebyselectively apply and relieve the application of the dampening force tothe seat.
 3. A vibration damper for a seat suspension system of a typewhich supports a seat above the floor of a vehicle, the seat beingraisable and lowerable to support the seat at various selectedelevations relative to the floor of the vehicle, and wherein movement ofthe seat from a selected elevation in response to vibration ispermitted; a first member adapted for coupling to one of the vehicle andseat; a shock absorber adapted to be coupled to the other of the vehicleand seat; and a latch adapted to selectively couple the first member tothe shock absorber such that when the shock absorber and first memberare coupled together the shock absorber applies a dampening force to theseat and when the shock absorber and first member are decoupled from oneanother the shock absorber is relieved from applying a dampening forceto the seat; wherein the shock absorber comprises a cylinder and a latchgripping surface carried by the cylinder; the shock absorber alsocomprising a dampening piston within the cylinder and a piston rodcoupled to the piston and having an end portion projecting outwardlyfrom the piston and which is adapted to be coupled to the other of thevehicle and seat; the latch comprising at least one latch arm includinga latch surface, the latch arm being coupled to the first member withthe latch arm being movable between first and second positions; andwherein when the latch arm is in the first position the latch surfaceand latch gripping surface engage one another to thereby couple theshock absorber to the first member and wherein when the latch arm is inthe second position the latch surface is disengaged from the latchgripping surface.
 4. A vibration damper according to claim 3 in whichthe latch gripping surface and latch surface each comprise at least onerow of teeth.
 5. A vibration damper according to claim 3 wherein thelatch arm is pivoted to the first member for pivoting movement betweenthe first and second positions.
 6. A vibration damper according to claim5 including a fluid actuator carried by the first member and coupled tothe latch arm for shifting the latch arm between the first and secondpositions.
 7. A vibration damper according to claim 5 in which the firstmember is pivotally coupled to said one of the vehicle and seat forpivoting about a first pivot axis and wherein the latch arm is pivotedto the first member for also pivoting about the first pivot axis.
 8. Avibration damper according to claim 5 wherein the cylinder is alsoslidably coupled to the first member for sliding movement relative tothe first member.
 9. A vibration damper according to claim 8 wherein thefirst member comprises a housing having a first side wall with anexterior surface at the exterior of the housing and an interior surfaceat the interior of the housing, the first side wall including first andsecond side wall portions spaced apart from one another to define aguide slot therebetween, a slide element mounted to the cylinder andslidably coupled to the first and second side wall portions such thatthe slide element slides along the guide slot and guides the slidingmotion of the cylinder relative to the housing.
 10. A vibration damperaccording to claim 9 in which the cylinder is substantially disposedwithin the housing, wherein the slide element includes first and secondinterconnected slide members which sandwich the respective first andsecond side wall portions therebetween, the first slide member beingpositioned substantially within the housing, the first slide memberincluding respective first and second teeth containing flange portionsextending in a direction away from the first side wall of the housing,the first and second teeth containing flange portions being spaced apartfrom one another and positioned at opposite sides of the center of thecylinder from one another, the latch arm having a generally U-shapedcross section with a base and first and second leg portions, the firstand second leg portions each terminating in an elongated row of teeth,the first and second leg portions each being aligned with a respectiveadjacent one of the first and second teeth supporting flange portions ofthe first slide member, and wherein the teeth of the first and secondleg portions engage the teeth of the respective adjacent flange portionswhen the latch arm is in the first position.
 11. A vibration damperaccording to claim 10 in which the housing includes a second wallopposite to the first wall, the second wall including an arm flangereceiving opening therein, the latch arm including an arm flangeprojecting from the base toward the arm flange receiving opening, anactuator guide flange projecting outwardly from the second wall of thehousing, the guide flange defining an actuator guide slot, a fluidactuator having an actuator cylinder which is pivoted to the housing, anactuator piston within the actuator cylinder and an actuator piston rodhaving an end portion projecting outwardly from the actuator cylinder, alink pivotally coupling the end portion of the actuator piston rod tothe latch arm flange, the end portion of the actuator piston rod alsobeing coupled to the actuator guide flange such that the actuator guideslot guides the movement of the actuator piston rod during extension andretraction of the actuator piston rod, wherein extension of the actuatorpiston rod shifts the latch arm to the second position, and retractionof the actuator piston rod shifts the latch arm to the second position.12. A vibration damper according to claim 11 wherein the shock absorberis adapted to provide a non-linear dampening force to the seat to dampenseat vibrations, the dampening force being constant for a first range ofmovement of the seat in response to vibrations from a home position ofthe dampening piston and increasing for certain movements of thedampening piston in excess of the first range of movement.
 13. Avibration damper according to claim 5 in which the first membercomprises a housing, the cylinder being substantially disposed withinthe housing, wherein the at least one latch arm comprises first andsecond latch arms pivoted to the housing and disposed at opposite sidesof the cylinder from one another, the first and second latch arms eachhaving a central portion and first and second end portions, the latcharms each being pivoted to the housing for pivoting movement about anaxis through the central portion of the latch arm, the first end portionof each latch arm including a latch surface, the cylinder having anexterior with elongated latch gripping surfaces positioned along thecylinder exterior and in position for selective engagement with thelatch surfaces carried by the latch arms, a fluid actuator having anactuator cylinder with an actuator piston contained in the actuatorcylinder and an actuator piston rod coupled to the actuator piston andextending outwardly from the actuator cylinder, a first link pivotallycoupling the actuator piston rod to the second end portion of the firstarm, a second link pivotally coupling the actuator piston rod to thesecond end portion of the second latch arm, wherein extension andretraction of the actuator piston rod pivots the respective first andsecond latch arms between respective first positions in which the latchsurfaces engage the latch gripping surfaces and second positions inwhich the latch surfaces are disengaged from the latch grippingsurfaces.
 14. A vibration damper according to claim 13, wherein thelatch gripping surface and latch gripping surfaces each comprise teeth.15. A vibration damper according to claim 13 wherein the shock absorberis adapted to provide a non-linear dampening force to the seat to dampenseat vibrations, the dampening force being constant for a first range ofmovement of the seat in response to vibrations from a home position ofthe dampening piston and increasing for certain movements in excess ofthe first range of movement.
 16. A vibration dampener for a seatsuspension system of a type which supports a seat above the floor of avehicle, the seat being raisable and lowerable to support the seat atvarious selected elevations relative to the floor of the vehicle, andwherein movement of the seat from a selected elevation in response tovibration is permitted, the vibration damper comprising: a shockabsorber which provides a dampening force in opposition to movement ofthe seat away from a selected elevation in response to vibrations, thedampening force being constant for a first range of movements of theseat in response to vibrations from a home position and increasing forcertain movements in excess of the first range of movements; and theshock absorber comprising an exterior housing, a piston positionedwithin the housing, and a piston rod projecting outwardly from thehousing, the piston rod being coupled to one of the seat or the vehiclefor applying the dampening force to the seat, and wherein the shockabsorber housing comprises a latch engaging surface.
 17. A vibrationdampener according to claim 16 in which the latch engaging surfacecomprises a teeth containing member mounted to the shock absorberhousing.
 18. A vibration dampener according to claim 16 including alatch adapted to selectively engage the latch surface to operativelycouple the shock absorber to the seat so as to apply a dampening forceto the seat and to selectively disengage the latch surface to decouplethe shock absorber from the seat so as to relieve the application of adampening force to the seat.
 19. A vibration dampener according to claim18 in which the shock absorber when operatively coupled to the seatprovides a dampening force in opposition to movement of the seat awayfrom a selected elevation in response to vibrations, the dampening forcebeing constant for a first range of movements of the seat in response tovibrations from a home position and increasing for certain movements inexcess of the first range of movements.
 20. A vibration dampener for aseat suspension system of a type which supports a seat above the floorof a vehicle, the seat being raisable and lowerable to support the seatat various selected elevations relative to the floor of the vehicle, andwherein movement of the seat from a selected elevation in response tovibration is permitted, the vibration damper comprising: a shockabsorber having an exterior housing, a piston positioned within thehousing, and a piston rod extending from the housing, the piston rodadapted for coupling to the seat for applying a dampening force to theseat, and wherein the shock absorber housing comprises a latch engagingsurface which is adapted for engagement by a latch to operatively couplethe shock absorber to the seat.
 21. A vibration damper for a seatsuspension system of the type which supports a seat above the floor of avehicle, the seat being raisable and lowerable to support the seat atvarious selected elevations relative to the floor of the vehicle, andwherein movement of the seat from a selected elevation in response tovibrations is permitted, the vibration damper comprising: a housingadapted for pivotal coupling to the floor of the vehicle; a shockabsorber adapted to be coupled to the seat; a latch adapted toselectively couple the housing to the shock absorber such that when theshock absorber and housing are coupled together the shock absorberapplies a dampening force to the seat and when the shock absorber andhousing are decoupled from one another the shock absorber is relievedfrom applying a dampening force to the seat; wherein the housing has aninterior and an exterior, the shock absorber being substantiallypositioned within the interior of the housing, and wherein the latch iscarried by the housing and selectively couples and decouples the shockabsorber to and from the housing to thereby selectively apply andrelieve the application of the dampening force to the seat; the shockabsorber having a cylinder and a latch gripping surface carried by thecylinder, the shock absorber also including a dampening piston withinthe cylinder and a piston rod coupled to the piston and having an endportion projecting outwardly from the piston and which is adapted to becoupled to the seat, the latch including first and second latch armseach including a latch surface, the latch arms being coupled to thehousing with the latch arms being movable between first and secondpositions, wherein when the latch arms are in the first position thelatch surface and latch gripping surfaces engage one another to therebycouple the shock absorber to the housing and wherein when the latch armsare in the second position the latch surfaces are disengaged from thelatch gripping surface; the latch gripping surface and latch surfaceeach comprising a plurality of teeth; the latch arms being pivoted tothe housing for pivoting movement between the first and secondpositions; a fluid actuator carried by the housing and coupled to thelatch arms for shifting the latch arms between the first and secondpositions; wherein the cylinder is also slidably coupled to the housingfor sliding movement relative to the housing; the housing having a firstside wall with an exterior surface at the exterior of the housing and aninterior surface at the interior of the housing, the first side wallincluding first and second side wall portions spaced apart from oneanother to define a guide slot therebetween, a slide element mounted tothe cylinder and slidably coupled to the first and second side wallportions such that the slide element slides along the guide slot andguides the sliding motion of the cylinder relative to the housing;wherein the slide element includes first and second interconnected slidemembers which sandwich the respective first and second side wallportions therebetween, the first slide member being positionedsubstantially within the housing, the first slide member includingrespective first and second teeth containing flange portions extendingin a direction away from the first side wall of the housing, the firstand second teeth containing flange portions being spaced apart from oneanother and positioned at opposite sides of the center of the cylinderfrom one another, the latch arm having a generally U-shaped crosssection with a base and first and second leg portions, the first andsecond leg portions each terminating in an elongated row of teeth, thefirst and second leg portions each being aligned with a respectiveadjacent one of the first and second teeth supporting flange portions ofthe first slide member, and wherein the teeth of the first and secondleg portions engage the teeth of the respective adjacent flange portionswhen the latch arm is in the first position; and wherein the housingincludes a second wall opposite to the first wall, the second wallincluding an arm flange receiving opening therein, the latch armincluding an arm flange projecting from the base toward the arm flangereceiving opening, an actuator guide flange projecting outwardly fromthe second wall of the housing, the guide flange defining an actuatorguide slot, a fluid actuator having an actuator cylinder which ispivoted to the housing, an actuator piston within the actuator cylinderand an actuator piston rod having an end portion projecting outwardlyfrom the actuator cylinder, a link pivotally coupling the end portion ofthe actuator piston rod to the latch arm flange, the end portion of -theactuator piston rod also being coupled to the actuator guide flange suchthat the actuator guide slot guides the movement of the actuator pistonrod during extension and retraction of the actuator piston rod, whereinextension of the actuator piston rod shifts the latch arm to the firstposition and retraction of the actuator piston rod shifts the latch armto the second position.
 22. A vibration damper for a seat suspensionsystem of the type which supports a seat above the floor of a vehicle,the seat being raisable and lowerable to support the seat at variousselected elevations relative to the floor of the vehicle, and whereinmovement of the seat from a selected elevation in response to vibrationsis permitted, the vibration damper comprising: a housing adapted forpivotal coupling to the floor of the vehicle; a shock absorber adaptedto be coupled to the seat; a latch adapted to selectively couple thehousing to the shock absorber such that when the shock absorber andhousing are coupled together the shock absorber applies a dampeningforce to the seat and when the shock absorber and housing are decoupledfrom one another the shock absorber is relieved from applying adampening force to the seat; wherein the housing has an interior and anexterior, the shock absorber being substantially positioned within theinterior of the housing, and wherein the latch is carried by the housingand selectively couples and decouples the shock absorber to and from thehousing to thereby selectively apply and relieve the application of thedampening force to the seat; the shock absorber having a cylinder and alatch gripping surface carried by the cylinder, the shock absorber alsoincluding a dampening piston within the cylinder and a piston rodcoupled to the piston and having an end portion projecting outwardlyfrom the piston and which is adapted to be coupled to the seat; thelatch including first and second latch arms each including a latchsurface, the latch arms being coupled to the housing with the latch armsbeing movable between first and second positions, wherein when the latcharms are in the first position the latch surface and latch grippingsurfaces engage one another to thereby couple the shock absorber to thehousing and wherein when the latch arms are in the second position thelatch surfaces are disengaged from the latch gripping surface; the latchgripping surface and latch surfaces each comprising a plurality ofteeth; the latch arms being pivoted to the housing for pivoting movementbetween the first and second positions; a fluid actuator carried by thehousing and coupled to the latch arms for shifting the latch armsbetween the first and second positions; wherein the latch arms aredisposed at opposite sides of the cylinder from one another, the firstand second latch arms each having a central portion and first and secondend portions, the latch arms each being pivoted to the housing forpivoting movement about an axis through the central portion of the latcharm, the first end portion of each latch arm including a latch surface,the cylinder having an exterior with elongated latch gripping surfacespositioned along the cylinder exterior and in position for selectiveengagement with the latch surfaces carried by the latch arms, a fluidactuator having an actuator cylinder with an actuator piston containedin the actuator cylinder and an actuator piston rod coupled to theactuator piston and extending outwardly from the actuator cylinder, afirst link pivotally coupling the actuator piston rod to the second endportion of the first arm, a second link pivotally coupling the actuatorpiston rod to the second end portion of the second latch arm, whereinextension and retraction of the actuator piston rod pivots therespective first and second latch arms between respective firstpositions in which the latch surfaces engage the latch gripping surfacesand second positions in which the latch surfaces are disengaged from thelatch gripping surfaces.
 23. A vibration dampener for a seat suspensionsystem of a type which supports a seat above the floor of a vehicle, theseat being raisable and lowerable to support the seat at variousselected elevations relative to the floor of the vehicle, and whereinmovement of the seat from a selected elevation in response to vibrationis permitted, the vibration damper comprising: a shock absorber whichprovides a dampening force in opposition to movement of the seat awayfrom a selected elevation in response to vibrations, the dampening forcebeing constant for a first range of movements of the seat in response tovibrations from a home position and increasing for certain movements inexcess of the first range of movements; the shock absorber comprises ahousing, a piston positioned within the housing and a piston rod; and ajack screw for adjusting the position of the housing relative to theseat without, during seat elevation adjustment, decoupling the shockabsorber from the seat.
 24. A vibration dampener for a seat suspensionsystem of a type which supports a seat above the floor of a vehicle, theseat being raisable and lowerable to support the seat at variousselected elevations relative to the floor of the vehicle, and whereinmovement of the seat from a selected elevation in response to vibrationis permitted, the vibration damper comprising: a shock absorber whichprovides a dampening force in opposition to movement of the seat awayfrom a selected elevation in response to vibrations, the dampening forcebeing constant for a first range of movements of the seat in response tovibrations from a home position and increasing for certain movements inexcess of the first range of movements; the shock absorber comprises ahousing, a piston positioned within the housing and a piston rod; and alatch adapted to selectively decouple the shock absorber from the seat.25. A vibration dampener for a seat suspension system of a type whichsupports a seat above the floor of a vehicle, the seat being raisableand lowerable to support the seat at various selected elevationsrelative to the floor of the vehicle, and wherein movement of the seatfrom a selected elevation in response to vibration is permitted, thevibration damper comprising: a shock absorber which provides a dampeningforce in opposition to movement of the seat away from a selectedelevation in response to vibrations; the shock absorber comprising ahousing, a piston positioned within the housing and a piston rod; theshock absorber when operatively coupled to the seat provides anon-linear dampening force in opposition to movement of the seat awayfrom a selected elevation in response to vibrations; a mechanism adaptedto adjust the position of the housing relative to the seat without,during seat elevation adjustment, decoupling the shock absorber from theseat; and the last named mechanism comprises a jack screw.